Water Pollution Practice Questions
20 free Water Pollution practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following is considered the primary cause of cultural eutrophication in water bodies?
- A Heavy metal accumulation from industries
- B Thermal discharge from power plants
- C Runoff rich in nitrates and phosphates
- D Oil spills from offshore drilling
Correct answer: Runoff rich in nitrates and phosphates
Cultural eutrophication is the accelerated aging of a water body due to human activities. Nutrient enrichment, specifically with nitrates and phosphates from agricultural runoff and sewage, leads to excessive algal growth and oxygen depletion.
Biochemical Oxygen Demand (BOD) is a measure of:
- A The amount of oxygen required by fish for respiration
- B Oxygen consumed to degrade organic matter in a water sample
- C The concentration of dissolved oxygen in pure water
- D The total amount of inorganic waste in a water body
Correct answer: Oxygen consumed to degrade organic matter in a water sample
BOD measures the amount of oxygen consumed by microorganisms to decompose organic matter in a unit volume of water. High BOD indicates high levels of organic pollution and lower water quality.
In a polluted river, which of the following changes is observed at the point of sewage discharge?
- A Sharp decline in dissolved oxygen and rise in BOD
- B Increase in dissolved oxygen and decrease in BOD
- C Increase in both dissolved oxygen and BOD
- D No change in dissolved oxygen but increase in fish population
Correct answer: Sharp decline in dissolved oxygen and rise in BOD
At the point of sewage discharge, the influx of organic matter triggers rapid microbial activity, which consumes dissolved oxygen. Consequently, the BOD rises sharply while the dissolved oxygen levels drop, often leading to fish mortality.
The phenomenon of biological magnification refers to the:
- A Increase in the size of organisms due to nutrient enrichment
- B Rising concentration of non-biodegradable toxicants at each trophic level
- C Rapid multiplication of algae in a nutrient-rich pond
- D Accumulation of biodegradable waste in the bodies of decomposers
Correct answer: Rising concentration of non-biodegradable toxicants at each trophic level
Biomagnification occurs because a toxic substance accumulated by an organism cannot be metabolized or excreted. As a result, the concentration of substances like DDT or mercury increases as they move up the food chain.
According to the NCERT, what is the concentration of DDT found in fish-eating birds if the water contains 0.003 ppb of DDT?
- A 0.5 ppm
- B 2 ppm
- C 25 ppm
- D 5 ppm
Correct answer: 25 ppm
Through biomagnification, DDT concentration increases significantly from water (0.003 ppb) to zooplankton, fish, and finally to fish-eating birds. In birds at the top of the food chain, the concentration can reach as high as 25 ppm.
High concentrations of DDT in birds interfere with calcium metabolism, leading to:
- A Decline in bird population from thinning of eggshells
- B Formation of thicker eggshells and delayed hatching
- C Increased appetite and metabolic rate
- D Immediate death of the adult birds
Correct answer: Decline in bird population from thinning of eggshells
DDT disrupts calcium deposition during eggshell formation in birds. This results in thin shells that break prematurely during incubation, ultimately leading to a decline in the bird population.
The 'Terror of Bengal' is an invasive aquatic weed known as:
- A Parthenium hysterophorus
- B Eichhornia crassipes
- C Lantana camara
- D Pistia stratiotes
Correct answer: Eichhornia crassipes
Eichhornia crassipes (Water Hyacinth) was introduced to India for its beautiful flowers but became a problematic invasive species. It grows rapidly in eutrophic water bodies and drains oxygen, leading to the death of fish.
Which method is specifically used for the remediation of heavy metal pollution in water by using plants?
- A Thermal incineration at high temperatures
- B Controlled pyrolysis treatment
- C Phytoremediation using specific absorbing plants
- D Biomagnification across food chain levels
Correct answer: Phytoremediation using specific absorbing plants
Phytoremediation involves using specific plants to absorb and accumulate heavy metals or other pollutants from contaminated water or soil. It is an eco-friendly and cost-effective remediation strategy.
What percentage of impurities makes domestic sewage unfit for human use?
- A 10% dissolved impurities
- B 5% dissolved impurities
- C 1% dissolved impurity
- D 0.1% impurities by volume
Correct answer: 0.1% impurities by volume
Domestic sewage consists of 99.9% water and only 0.1% impurities. These impurities include suspended solids, colloidal materials, and dissolved nutrients like nitrates and phosphates.
Thermal wastewater discharge into water bodies primarily affects the ecosystem by:
- A Increasing the nutrient content of the water
- B Decreasing the BOD of the water
- C Lowering dissolved oxygen and harming cold-water organisms
- D Promoting the growth of indigenous aquatic species
Correct answer: Lowering dissolved oxygen and harming cold-water organisms
Heated effluents from power plants raise the water temperature, which reduces the solubility of oxygen. This thermal pollution can eliminate organisms sensitive to high temperatures and disrupt the natural biological balance.
Which of the following is a result of the excessive growth of planktonic algae in a water body?
- A Improvement in water quality and clarity
- B Dense algal bloom formation
- C Decrease in BOD levels
- D Increased transparency of water
Correct answer: Dense algal bloom formation
Algal blooms are caused by high levels of nutrients in the water, leading to the rapid proliferation of algae. This often imparts a distinct color to the water and can cause the release of toxins harmful to aquatic life.
The ‘Arcata Marsh’ project in California is a famous example of:
- A Integrated wastewater treatment
- B Solid waste management
- C Radioactive nuclear waste disposal methods
- D Reforestation
Correct answer: Integrated wastewater treatment
The Arcata Marsh project combined conventional sedimentation and filtration with a series of six marshes. The marshes acted as natural filters where plants, algae, and bacteria purified the water of heavy metals and nutrients.
What is 'EcoSan' as mentioned in the context of environmental issues?
- A An ecological survey of wildlife sanctuaries
- B A dry composting toilet system for sustainable waste management
- C A chemical disinfectant-based sanitation method
- D A software platform for monitoring water pollution levels
Correct answer: A dry composting toilet system for sustainable waste management
Ecological sanitation (EcoSan) is a sustainable approach that uses dry composting toilets to recycle human excreta into natural fertilizer. This method saves water and prevents the pollution of water bodies by sewage.
Minamata disease was caused by the consumption of fish contaminated with:
- A Cadmium
- B Lead
- C Mercury
- D Arsenic
Correct answer: Mercury
Minamata disease is a neurological syndrome caused by severe mercury poisoning. It occurred in Japan after industrial wastewater containing methylmercury was discharged into Minamata Bay and accumulated in fish.
The Water (Prevention and Control of Pollution) Act was passed by the Government of India in:
- A 1981
- B 1986
- C 1974
- D 1990
Correct answer: 1974
The Water Act was enacted in 1974 to prevent and control water pollution and maintain or restore the wholesomeness of water in the country. It led to the establishment of Central and State Pollution Control Boards.
Polyblend, a fine powder of recycled modified plastic, was mixed with bitumen to:
- A Treat industrial wastewater
- B Construct more durable roads
- C Fertilize agricultural fields
- D Clean oil spills in the ocean
Correct answer: Construct more durable roads
Developed by Ahmed Khan, Polyblend is used to enhance the water-repellent properties of bitumen. When used in road construction, it increases the road's life by a factor of three.
Which of the following heavy metals is associated with the 'Itai-itai' disease?
- A Mercury
- B Arsenic
- C Cadmium
- D Lead
Correct answer: Cadmium
Itai-itai disease is caused by chronic cadmium poisoning, often through contaminated water used for irrigation. It causes softening of the bones and kidney failure.
Blue baby syndrome (Methaemoglobinaemia) is caused by the contamination of drinking water with excess:
- A Fluoride
- B Nitrate
- C Chloride
- D Sulphate
Correct answer: Nitrate
Nitrates in drinking water are converted to nitrites by bacteria in the digestive tract. Nitrites bind to hemoglobin, forming methaemoglobin, which reduces the blood's oxygen-carrying capacity, particularly in infants.
The process where a water body dies due to the accumulation of silt and organic debris over thousands of years is called:
- A Biomagnification
- B Natural Eutrophication
- C Accelerated Eutrophication
- D Greenhouse effect
Correct answer: Natural Eutrophication
Natural eutrophication is the slow, geological process of a lake aging. Over time, the lake becomes shallower and warmer as organic remains and silt fill the basin, eventually transforming it into land.
A river with a very high BOD value is likely to be:
- A Highly polluted and oxygen-depleted from organic waste
- B Very clean and rich in dissolved oxygen
- C Highly saline due to industrial discharge
- D Naturally rich in dissolved calcium, magnesium, and mineral salts
Correct answer: Highly polluted and oxygen-depleted from organic waste
High BOD indicates that a large amount of organic matter is present, requiring significant oxygen for decomposition. This status is characteristic of highly polluted water bodies where dissolved oxygen levels are typically very low.